In the related art, as a circuit module, a pluggable module is known which can be inserted into or removed from a main body of an apparatus during the operation of the apparatus. For example, the pluggable module is an electro-optical conversion module which is mounted on a server apparatus, a router, a switch, or the like that are used for optical communication.
In a case where the pluggable module is inserted into the apparatus main body, a large current is likely to instantaneously flow from the apparatus main body into the pluggable module at the time when the pluggable module is activated. In this manner, the large current which instantaneously flows from the apparatus main body into the pluggable module at the time when the pluggable module is inserted into the apparatus main body is referred to as an inrush current.
In some cases, the occurrence of the inrush current may have a negative influence on other pluggable modules which have been already inserted into the apparatus main body. More specifically, when pluggable modules are inserted into the apparatus main body, the pluggable modules use a power supply installed in the apparatus main body as a common power supply. Therefore, for example, when a new pluggable module is further inserted into the apparatus main body, the current flowing from the apparatus main body into that pluggable module instantaneously increases due to the inrush current caused by the activation of the pluggable module. As a result, the power supply voltage of the apparatus main body temporarily decreases, and thus an operation failure may occur on the other pluggable modules which share the power supply.
In this mariner, the inrush current caused by the insertion of the pluggable module into the apparatus main body may negatively affect the other pluggable modules. Therefore, in order to prevent the occurrence of this problem, the rate of change in the current flowing into the pluggable module is set according to a standard, in such a manner that the rate of change is always equal to or less than a predetermined value (for example, 50 mA/mSec). This technique has been known as disclosed in, for example, “XENPAK 10 Gigabit Ethernet MSA, A Cooperation Agreement for 10 Gigabit Ethernet Transceiver Package, Issue 3.0”, [online], [searched on Mar., 25, 2009], Internet <URL:http://www.cotsworks.com/PDFs/XENPAK_MSA_R3.0%5B1%5D.p df>).
Therefore, in some cases, an inrush current control unit for preventing the occurrence of the inrush current may be installed in the pluggable module. The inrush current control unit is, for example, a hot swap controller (Product No.: LTC4210) manufactured by Linear Technology Corporation, or the like. The inrush current control unit limits the inrush current by gradually decreasing a resistance value of an FET provided on the power supply line from the maximum value thereof.
However, in some cases, the occurrence of the inrush current may not be sufficiently suppressed only by the control of the inrush current control unit of the related art.
For example, when a circuit that has a power-on reset function is provided in the pluggable module, the inrush current may still occur even if the inrush current is controlled by the inrush current control unit of the related art.
The power-on reset function is a process for turning off the electrical state of the circuit during a period between the power-on time and the time when a predetermined reset time passes in order to prevent the occurrence of a problem caused by the operation of the circuit until the time when the power supply voltage reaches a target value. FIG. 13 illustrates the state in which a plurality of pluggable modules is inserted into the apparatus main body in the related art.
As illustrated in FIG. 13, a plurality of pluggable modules 600a to 600n is inserted into an apparatus main body 500 that includes a power supply 510. The pluggable module 600a includes a circuit 601 that does not have the power-on reset function (hereinafter, simply referred to as “circuit”), a control object circuit 602a that has the power-on reset function, and a control object circuit 602b that is a thermoelectric cooler (TEC) circuit that controls a temperature. In addition, the pluggable module 600a includes a laser diode (hereinafter, “LD”) 603, a power supply activation control unit 604, a hot swap controller 605, and a field effect transistor (hereinafter, “FET”) 606. The power supply activation control unit 604 controls the supplying and blocking of the current to the circuit 601 and the control object circuits 602a and 602b. The hot swap controller 605 corresponds to the inrush current control unit and limits the inrush current by gradually decreasing the resistance value of the FET 606 provided on the power supply line from the maximum value thereof.
The control object circuit 602b includes a temperature control unit 611, a TEC driver 612, and a TEC 613. The temperature control unit 611 is a control unit which controls the temperature of the LD 603. The temperature control unit 611 outputs a control signal for adjusting the temperature of the LD 603 to a set temperature to the TEC driver 612. The TEC driver 612 supplies a current to the TEC 613 on the basis of the control signal output from the temperature control unit 611. The TEC 613 is a thermoelectric conversion device that adjusts the temperature of the LD 603. The TEC 613 converts the power supplied from the TEC driver 612 into heat to adjust the temperature of the LD 603.
FIG. 14 is a graph illustrating a temporal change of the voltage and the current in the pluggable module 600a of the related art. In addition, as illustrated in FIG. 13, the power supply voltage of the apparatus main body 500 is denoted by V0; the control voltage of the resistance value of the FET 606 provided on the power supply line is denoted by V1; the power supply voltage in the pluggable module 600a is denoted by V2; and the voltage for starting the operation of the control object circuit 602a is denoted by V4. Similarly, the current flowing into the circuit 601 is denoted by I5; the current flowing into the control object circuit 602a is denoted by I7; the currents flowing into the pluggable modules 600a to 600n are respectively denoted by I8a to I8n; and the current flowing into the control object circuit 602b is denoted by I12.
As illustrated in FIG. 14, when the pluggable module 600a is inserted into the apparatus main body 500 at t1, the hot swap controller 605 gradually increases the voltage V1 applied to the FET 606 to gradually decrease the resistance value of the FET 606. Accordingly, because the power supply voltage V2 and the current I8a in the pluggable module 600a are gradually increased without a rapid increase, the occurrence of the inrush current is limited at the time of starting the circuit.
On the other hand, the control object circuit 602a that has the power-on reset function is in the state in which the current is blocked by the power supply activation control unit 604 until the power supply voltage V2 in the pluggable module 600a reaches a target voltage (for example, ±5% of a rated value). Next, when the power supply voltage V2 in the pluggable module 600a reaches the target voltage and a predetermined reset period elapses, the power supply activation control unit 604 applies the voltage V4 for starting the operation of the control object circuit 602a to the control object circuit 602a. Accordingly, the current I7 starts to flow into the control object circuit 602a at once in response to the start of the operation.
In other words, as illustrated in FIG. 14, when the voltage V4 is applied to the control object circuit 602a at t2, the current I7 starts to flow into the control object circuit 602a at once, and thus the current I8a flowing into the entirety of the pluggable module 600a also rapidly increases. As a result, in some cases, the power supply voltage VO of the apparatus main body 500 is temporarily decreased, and thus an operation failure may occur on the other pluggable modules 600b to 600n . 
In this manner, because a circuit that has the power-on reset function starts the operation at once at the time when a predetermined reset period elapses, the inrush current control unit of the related art may not solve the problem. Therefore the inrush current may occur in the related art. In other words, the inrush current control unit of the related art may not meet the standard that the rate of change rate in the current flowing into a pluggable module is equal to or less than a predetermined value.